In honor of MarkCC’s latest effort to explain to the deeply egnorant Michael Egnor why the fact that any inferentially true set of statements – including scientific theories – can be reformulated as a tautology, I thought I’d crack open Elliot Sober’s excellent Philosophy of Biology, in which he discusses the relevance of the “tautology” objection to evolution. But before doing that, I have to take exception to something Egnor said. I actually take exception to nearly everything he says, but I’d rather not bog down in the details. Egnor tries to summarize natural selection as “survivors survive,” but that is not at all the issue.
Just as Newton’s first law states that an object at motion tends to stay in motion (all else being equal), natural selection states that the offspring of survivors will tend to survive (all else being equal). This statement, on its own, is not any sort of tautology. Even “survival of the fittest,” is not tautological in the strict sense of the term.
Sober explains this point thusly:
Before I address the criticism, the term “tautology” needs to be clarified. The first important point is that propositions are the only things that are tautologies. Not all propositions are tautologies, but all tautologies are propositions. A proposition is what is expressed by a declarative sentence in some language; it is either true or false. But notice that the phrase “the survival of the fittest” is not a declarative sentence. If we are going to assess whether “the survival of the fittest” is a tautology, we first must be precise about which proposition we wish to examine.
After discussing the formal logical statements that are always tautological (P or not‑P, etc.), Sober observes that people sometimes refer to a statement as tautology because of the meanings of the words in the sentence. “All bachelors are unmarried” does not have a logical structure that makes it tautological; “all x are y” is only true because we know something about x and y. Because we know that a bachelor is an unmarried man, we can understand that the statement must be true. Sentences which can be evaluated for truth or falsity based on definitions are called analytic, those which require other information are referred to as synthetic.
We have to reformulate “survival of the fittest” into a different form, then, to know if it is tautological. Egnor seems to think it translates to “all survivors survive,” which turns out to be neither accurate nor true. As the Boss says, “everything dies, baby that’s a fact.”
Sober reformulates it as “The traits found in contemporary populations are present because those populations were descended from ancestral populations in which those traits were the fittest of the variants available.” Egnor might want to summarize that statement as “survivors have traits which they pass on to future generations.” As Sober observes:
this statement is not a tautology; it is not a truth of logic that present populations were descended from ancestral populations. This implication of the statement is true enough, but it is no tautology. The second thing to notice is that the statement, taken as a whole, is false. A trait now at fixation in some population may have reached fixation for any number of reasons. Natural selection is one possible cause, but so are random genetic drift, mutation and migration.
Incidentally, it is a curiosity of some creationist argumentation that evolutionary theory is described as being (1) untestable, (2) empirically disconfirmed, and (3) a tautology. This nested confusion to one side, the main point here is that the statement displayed above is not a tautology and, in any case, is not part of the theory of evolution. Far from being an analytic truth, it is a synthetic falsehood.
As Sober goes on to point out, the theory of evolution may well contain some tautologies. For instance, defining fitness is complicated, and one can formulate definitions which would be tautological. He goes on to note that “the fact that the theory of evolution contains this tautology does not show that the whole theory is a tautology. Don’t confuse the part with the whole. Perhaps what is most preposterous about the “tautology problem” is that it has assumed that the status of the whole theory depends on the verdict one reaches about one little proposition.”
Later, Sober observes that physical laws tend to be empirical claims (eg, mass attracts mass) while evolutionary laws (like the Hardy-Weinberg equilibrium) “once … stated carefully, … often turns out to be a (nonempirical) mathematical truth.” Thus, if natural selection is a tautology, it is one in the same sense that a good mathematical proof is tautological. Referring to something as tautology generally means it is trivial. This broad sense easily encompasses non-trivial insights which are true by virtue of logical analysis, not on any empirical basis. Unless being true has suddenly become a bad thing, I’m comfortable with knowing natural selection and other mathematical models in biology can be constructed as a mathematical truths.